Conventional analog-to-digital converters (ADCs) are fabricated using electronic integrated circuits. The function of an ADC is to repeatedly sample a time-varying analog signal, generally at fixed time intervals, and to generate a digital representation of the analog signal with a certain level of precision. The precision of electronic ADCs is limited to an effective number of bits (ENOB) that decreases with increasing frequency.
Electronic ADCs are frequently used to convert optical analog signals to optical digital signals. In order to employ an electronic ADC in such a conversion, the optical analog signal is converted to an electrical analog signal, the electrical analog signal is then converted to a electrical digital signal, and the electrical digital signal is finally converted to optical digital signal. The optical to electrical and electrical to optical conversions degrade signal fidelity and power. Optical ADCs promise to overcome the limitations of electronic ADCs and to provide an improved speed and resolution for the digitization of optical analog signals.